1. Field of the Invention
The invention relates to a developing device for serial electrostatic printing of alphanumeric characters on a record carrier, in which the latent image is brought into contact, immediately after printing, with developer which is applied to the record carrier by a rotatable magnetic roller which is arranged parallel to the record carrier.
2. Description of the Prior Art
Known electrostatic writing methods have an annoying aspect in that the latent images become visible only after departure from the developing chamber, i.e. after the record carrier has been further transported over several lines. In order to solve this problem, in a known line printer the developing chamber filled with toner mixture is arranged underneath the printing station and a rotatably journalled magnet is mounted at the rear of the record carrier, so that part of the toner mixture is pulled upwards at the area of the printing station as soon as the line has been printed (German Offenlegungsschrift No. 2,064,036).
Also known is a serial printing device in which the printing head is step-wise moved over the record carrier, the head being continuously present in the developing mixture. A magnetic brush is rotatably arranged parallel to the printing head guide over the full width of the record carrier, so that the developing mixture is continuously in contact with the record carrier at the area of the printing line (German Offenlegungsschrift No. 2,125,081). However, in this serial printing device the printed line again becomes visible only after the record carrier has been transported one line further.
In both known devices the possibility of making the images quickly visible exists because of bringing the electrode pins directly into contact with the developer. However, fast contamination of the printing heads is then unavoidable.